Portable devices capable of indicating level, plumb and square alignment have been useful in the construction and carpentry trades for some time. The advent of laser technology has seen the use of portable laser emitting devices capable indicating level and plumb, as well as level, plumb and square alignments simultaneously.
In some prior art tools, alignment is indicated with beams that form points of light or “spots” on a surface against which they are projected. In some prior art tools, an invisible “line” can be imagined between two or more opposing and aligned spots to provide an alignment line. Other tools indicate alignment with beams that form the image of a straight line on the surface against which they are projected, that is, they project linear alignment beams.
Such devices typically require some sort of tilt-compensation mechanism or self-leveling mechanism, to avoid the introduction of error when operated from a non-level surface. However, even with a tilt-compensation or self-leveling mechanism, such tools typically can only accurately indicate level and plumb within a range of inclinations of the tool relative to level. To avoid a user inadvertently relying on an erroneous indication of alignment, some tools provide an indication to the user, when the user is attempting to use the tool outside of a predefined range of inclinations, for example, by ceasing projection of alignment beams or causing the alignment beams to blink.